El Niño conditions developed over the past month, as shown by above-average sea surface temperatures (SSTs) across the central to eastern equatorial Pacific Ocean [Fig. 1]. The latest weekly Niño-3.4 index value was +0.7°C, with the westernmost (Niño-4) and easternmost (Niño-1+2) indices at +0.7°C and +2.1°C, respectively [Fig. 2]. The equatorial subsurface temperature index (average from 180°-100°W) decreased in the past month [Fig. 3], but significantly above-average subsurface temperatures remained in the central and eastern equatorial Pacific [Fig. 4]. Low-level westerly wind anomalies and upper-level easterly wind anomalies were evident over the central equatorial Pacific. Convection was slightly above average over the central and east-central equatorial Pacific and was near or below average over Indonesia [Fig. 5]. The traditional and equatorial Southern Oscillation indices were negative. Collectively, the coupled ocean-atmosphere system reflected the onset of El Niño conditions.

The North American Multi-Model Ensemble (NMME) average, including the NCEP CFSv2 [Fig. 6], forecasts El Niño to intensify into the Northern Hemisphere winter 2026-27. High confidence in El Niño [Fig. 7] is also linked to anomalously high oceanic heat content and expanding westerly wind anomalies across the equatorial Pacific Ocean. There is a 63% chance of a very strong El Niño during November-January [Fig. 8] that would rank among the largest El Niño events in the historical record going back to 1950. Even very strong El Niño events do not lead to the expected impact everywhere, but stronger events can more significantly tilt the odds in favor of expected outcomes (see CPC outlooks for probabilities of seasonal anomalies). In summary, El Niño conditions are present and expected to strengthen into the Northern Hemisphere winter 2026-27.